Battery

Abstract

A positive electrode active material that inhibits a decrease in discharge capacity in charge and discharge cycles and a battery using the positive electrode active material are provided. A high-safety battery is provided. The battery includes a positive electrode including a positive electrode current collector and a positive electrode active material layer. The positive electrode current collector is a carbon sheet. The positive electrode active material contains lithium cobalt oxide containing nickel and magnesium. The detected amount of nickel in a surface portion of the positive electrode active material is larger than that in an inner portion of the positive electrode active material. The detected amount of magnesium in the surface portion of the positive electrode active material is larger than the detected amount of magnesium in the inner portion of the positive electrode active material. The surface portion in the positive electrode active material includes a region where the distribution of nickel and the distribution of magnesium overlap with each other.

What is claimed is: 
     
         1 . A battery comprising a positive electrode,
 wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer, and   wherein the positive electrode current collector is a carbon sheet.   
     
     
         2 . The battery according to  claim 1 , wherein the carbon sheet comprises carbon nanotubes. 
     
     
         3 . The battery according to  claim 1 ,
 wherein the positive electrode active material layer comprises a positive electrode active material,   wherein the positive electrode active material comprises lithium cobalt oxide comprising nickel and magnesium,   wherein a detected amount of nickel in a surface portion of the positive electrode active material is larger than a detected amount of nickel in an inner portion of the positive electrode active material,   wherein a detected amount of magnesium in the surface portion of the positive electrode active material is larger than a detected amount of magnesium in the inner portion of the positive electrode active material, and   wherein the surface portion of the positive electrode active material comprises a region where distribution of nickel and distribution of magnesium overlap with each other.   
     
     
         4 . The battery according to  claim 3 , wherein nickel is detected on a plane other than a (001) plane of lithium cobalt oxide in the surface portion of the positive electrode active material. 
     
     
         5 . A battery comprising a positive electrode,
 wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer,   wherein the positive electrode current collector comprises a stack of a first carbon sheet and a second carbon sheet, and   wherein the first carbon sheet and the second carbon sheet each comprise carbon nanotubes.   
     
     
         6 . The battery according to  claim 5 ,
 wherein in the first carbon sheet, the carbon nanotubes are oriented in a first direction parallel to a surface of the first carbon sheet,   wherein in the second carbon sheet, the carbon nanotubes are oriented in a second direction parallel to a surface of the second carbon sheet, and   wherein the first direction and the second direction are substantially orthogonal to each other.   
     
     
         7 . The battery according to  claim 5 ,
 wherein the battery comprises an exterior body surrounding the positive electrode and a positive electrode lead extending from an inside to an outside of the exterior body, and   wherein the positive electrode lead comprises a region positioned between the first carbon sheet and the second carbon sheet.   
     
     
         8 . The battery according to  claim 5 ,
 wherein the positive electrode active material layer comprises a positive electrode active material,   wherein the positive electrode active material comprises lithium cobalt oxide comprising nickel and magnesium,   wherein a detected amount of nickel in a surface portion of the positive electrode active material is larger than a detected amount of nickel in an inner portion of the positive electrode active material,   wherein a detected amount of magnesium in the surface portion of the positive electrode active material is larger than a detected amount of magnesium in the inner portion of the positive electrode active material, and   wherein the surface portion of the positive electrode active material comprises a region where distribution of nickel and distribution of magnesium overlap with each other.   
     
     
         9 . The battery according to  claim 8 , wherein nickel is detected on a plane other than a (001) plane of lithium cobalt oxide in the surface portion of the positive electrode active material. 
     
     
         10 . The battery according to  claim 9 , wherein in EDX line analysis, a difference between a depth of a peak of the detected amount of nickel and a peak of the detected amount of magnesium in the surface portion of the positive electrode active material is less than or equal to 3 nm. 
     
     
         11 . The battery according to  claim 8 ,
 wherein the positive electrode active material comprises aluminum,   wherein in EDX line analysis of nickel, magnesium, and aluminum in the positive electrode active material, a maximum value of a detected amount of aluminum is observed at an inner portion than a maximum value of a detected amount of nickel and a maximum value of a detected amount of magnesium, and   wherein in EDX line analysis, when a peak width at a height that is ⅕ of a height of the maximum value of the detected amount of aluminum is divided into two parts by a perpendicular extending from the maximum value to a horizontal axis, a peak width W c  on an inner portion side is larger than a peak width W s  on a surface side.   
     
     
         12 . The battery according to  claim 8 ,
 wherein the lithium is used for the positive electrode and a counter electrode, and   wherein when the positive electrode is analyzed by powder X-ray diffraction using a CuKα 1  ray in a state where the battery is charged to 4.6 V, a diffraction pattern of the positive electrode active material comprises at least a first peak at 2θ of greater than or equal to 19.13° and less than 19.37° and a second peak at 2θ of greater than or equal to 45.37° and less than 45.57°.   
     
     
         13 . The battery according to  claim 8 ,
 wherein the positive electrode active material comprises fluorine, and   wherein a detected amount of fluorine in the surface portion of the positive electrode active material is larger than a detected amount of fluorine in the inner portion of the positive electrode active material.   
     
     
         14 . A battery comprising a positive electrode,
 wherein the positive electrode comprises a positive electrode current collector and a positive electrode active material layer,   wherein the positive electrode current collector comprises a stack of a first carbon sheet and a second carbon sheet,   wherein the first carbon sheet and the second carbon sheet each comprise carbon nanotubes,   wherein in the first carbon sheet, the carbon nanotubes are oriented in a first direction parallel to a surface of the first carbon sheet,   wherein in the second carbon sheet, the carbon nanotubes are oriented in a second direction parallel to a surface of the second carbon sheet,   wherein the first direction and the second direction are substantially orthogonal to each other,   wherein the positive electrode active material layer comprises a positive electrode active material,   wherein the positive electrode active material comprises lithium cobalt oxide comprising nickel and magnesium,   wherein a detected amount of nickel in a surface portion of the positive electrode active material is larger than a detected amount of nickel in an inner portion of the positive electrode active material,   wherein a detected amount of magnesium in the surface portion of the positive electrode active material is larger than a detected amount of magnesium in the inner portion of the positive electrode active material, and   wherein the surface portion of the positive electrode active material comprises a region where distribution of nickel and distribution of magnesium overlap with each other.   
     
     
         15 . The battery according to  claim 14 ,
 wherein the battery comprises an exterior body surrounding the positive electrode and a positive electrode lead extending from an inside to an outside of the exterior body, and   wherein the positive electrode lead comprises a region positioned between the first carbon sheet and the second carbon sheet.   
     
     
         16 . The battery according to  claim 14 , wherein nickel is detected on a plane other than a (001) plane of lithium cobalt oxide in the surface portion of the positive electrode active material. 
     
     
         17 . The battery according to  claim 14 , wherein in EDX line analysis, a difference between a depth of a peak of the detected amount of nickel and a peak of the detected amount of magnesium in the surface portion of the positive electrode active material is less than or equal to 3 nm. 
     
     
         18 . The battery according to  claim 14 ,
 wherein the positive electrode active material comprises aluminum,   wherein in EDX line analysis of nickel, magnesium, and aluminum in the positive electrode active material, a maximum value of a detected amount of aluminum is observed at an inner portion than a maximum value of a detected amount of nickel and a maximum value of a detected amount of magnesium, and   wherein in EDX line analysis, when a peak width at a height that is ⅕ of a height of the maximum value of the detected amount of aluminum is divided into two parts by a perpendicular extending from the maximum value to a horizontal axis, a peak width W c  on an inner portion side is larger than a peak width W s  on a surface side.   
     
     
         19 . The battery according to  claim 14 ,
 wherein the lithium is used for the positive electrode and a counter electrode, and   wherein when the positive electrode is analyzed by powder X-ray diffraction using a CuKα 1  ray in a state where the battery is charged to 4.6 V, a diffraction pattern of the positive electrode active material comprises at least a first peak at 2θ of greater than or equal to 19.13° and less than 19.37° and a second peak at 2θ of greater than or equal to 45.37° and less than 45.57°.   
     
     
         20 . The battery according to  claim 14 ,
 wherein the positive electrode active material comprises fluorine, and   wherein a detected amount of fluorine in the surface portion of the positive electrode active material is larger than a detected amount of fluorine in the inner portion of the positive electrode active material.